This invention concerns a method for the local composting and drying of organic wastes and device therefor.
The invention is used in the field of the collection and conversion of solid or muddy organic wastes advantageously mixed with sawdust or another material which ensures the permeability of air so as to provide a finished product known in the art as "compost".
This finished product, compost, is commonly used in the agricultural field to enrich and to fertilise land intended for cultivation.
The invention makes possible a localised conversion on the spot of the collected organic wastes or wastes produced at the same place, thus avoiding recourse to specific composting plants of great sizes.
By composting the wastes is meant the aerobic degradation of biodegradable material in the form of wastes so as to obtain a finished product mainly intended for use as a product for agricultural improvement.
The conversion and stabilisation of organic wastes known as composting have to take place in the presence of oxygen, and, for a good conversion to be achieved, anaerobic conditions should not take place.
The most active step in the composting of wastes is carried out under conditions of forced ventilation and may last from a minimum of 5 to 7 days to a maximum of about 15 to 20 days depending on the type of the wastes, the quantity of air employed, the outside atmospheric conditions, etc.
So as to speed up the degradation of the biodegradable organic material, the wastes are advantageously, but not necessarily, ground beforehand into particles of small sizes.
The muddy biodegradable wastes such as those arising from the purification of urban waste waters, can be composted by being mixed with sawdust, wood chips or another-material which makes the mass of the wastes permeable to air.
According to the state of the art the humidity content in the mass of wastes is stabilised at a value of about 50 to 60% so that the biological activity can proceed at the best speed.
Moreover, if it is necessary to make the composting process proceed at a greater speed, to the mass of wastes may be added solutions having a high nitrogen content so that the carbon:nitrogen ratio is adjusted to an optimum value estimated to be about 35:45.
In the state of the art the processes of composting the organic wastes are carried out in appropriate specifically designed plants generally equipped with collecting and containing vessels of great sizes in which the conversion and degradation of the collected wastes are performed.
The operators of such plants typically carry out the collection of the wastes, the transporting of those wastes to the specific composting plant, the possible sorting of the wastes, the conversion and exploitation thereof and the possible marketing of the finished compost.
All the above processes entail great expenses, above all for firms of small and medium sizes, for instance firms in the foodstuffs field, which produce organic wastes in great quantities and have to make use of the operators of such plants for the disposal and treatment of the wastes.
Considerable expenses are also borne by the community in general, which has to incur the burden of the collection and conversion of its own organic wastes as performed exclusively in such specialised plants.
With regard to the evermore active tendency towards the differentiated collection of wastes, which will lead, and in some countries already leads, to more and more strict regulations regarding the upstream sorting of wastes on the basis of their type, it will be possible in the near future to perform the differentiated collection of organic wastes which can be used at once for composting treatment.